Month: December 2016

Sending mail with an ESP8266 can be handy for a variety of things. I use it to occasionally have a remote ESP8266 send me a message it is still ok and functioning.
Though it is possible to have the ESP8266 directly access your mail server and send a message through that, that is usually not a good idea as many mailservers will refuse mail that is being sent from a different domain (your ip) than the mailserver’s.
it is therefore safer to use a service like smtp2go.com. As long as you stay below a certain limit of emails, one can get a free account.

After signing up for smtp2go, you will need to choose a user id and password for your smtp log in. You thus have two sets of id and password: one for your user account and one for the mails you send.
The latter, you need to encode in base 64 to use from your ESP8266. You can do that with an online encoder.
As there is no need to re-invent the wheel, I used this program as a basis and reworked that to my needs, but as your needs might be different from mine, I will just give a general example.
In order to send something more useful than ‘Hello World’, we are going to send the supply voltage and the chip ID. In real life I do not send the suply voltage as that is not so useful, but I send the battery voltage. But to keep it simple in this example we will stick to the supply voltage, which we get with ESP.getVcc().
The program is like this: (NOTE: the code might be badly formatted by wordpress, make sure you copy it completely)

In the example I use “gmail” but ofcourse this can be any other mailservice>
In the program you will also see a line with “yrmail@gmail.com"));// not important“. I may be wrong but it is not that important what that says. It is the identity under which your mails are grouped in the smpt2go dashboard. Maybe it is easiest to make that equal to the sender address, but it isnot important for the functioning of the program.

The strings that are send are rather flexible. Instead ofclient.println(F("Subject: Emails from ESp8266\r\n"));
On can also do:client.print(F("Subject: "));
if (condition == met)
client.println(F(PREDEFINED_MESSAGE));

There are a million reasons why you would want to monitor the Battery voltage of your Battery fed ESP8266. I will illustrate it with a Wemos D1 mini and the Battery shield

Wemos D1 Mini Battery shield

I am using a small 720 mAh LiPo cel. If I just leave the Wemos access the internet continuously it will last 6.5 hours, but for this example I will put the Wemos in Deepsleep for a minute, then read the battery voltage and upload that to Thingspeak.
You only need to make a few connections:
First, connect RST with GPIO16 (that is D0 on the Wemos D1 mini). This is needed to let the chip awake from sleep.
Then connect the Vbat through a 100k resistor to A0.

So why a 100 k resistor?

Well the Wemos D1 mini already has an internal voltage divider that connects the A0 pin to the ADC of the ESP8266 chip. This is a 220 k resistor over a 100 k resistor

Wemos D1 Internal Voltage divider

By adding a 100k , it will in fact be a total resistance of 100k+220k+100k=420k.
So if the Voltage of a fully loaded Cell would be 4.2 Volt, the ADC of the ESP8266 would get 4.2 * 100/420= 1 Volt

1 Volt is the max input to the ADC and will give a Raw reading of 1023.

The True voltage then can be calculated by:
raw = AnalogRead(A0);voltage =raw/1023;
voltage =4.2*voltage;
Ofcourse you could also do that in one step, but I like to keep it easy to follow.

Wemos Battery monitoring

If you do use this possibility, do realise that the resistors drain the battery as well with a constant 10uA (4.2V/420 000ohm). The powerconsumption of an ESP8266 in deepsleep is about 77uA. With the battery monitor this would be 87uA, which is a sizeable increase. A solution could be to close off the Vbat to the A0 with a transistor, controlled from an ESP8266 pin

The new battery shield
There now is a new version (V1.2.0) of the battery shield that has an inbuilt resistor connecting A0 to the battery, through Jumer J2 (‘Jumper’ being a big word for 2 solderpads), so if you want to measure the battery voltage, all you need to do is to put some solder connecting J2
However, rather than a 100k resistor, a 130k resistor was used. The voltage divider thus becomes 100/(130+220+100), so for a full reading of 1023 (=1Volt on A0) a total of (1/100k)*(130+220+100)=4.5Volt would be necessary.
In reality the Lipo cell will not give off 4.5Volt.